Katherine Clark, Stephen J. Quinn, Matthew Doogue, Christine Sanderson, Melanie Lovell, David C. Currow

Neuropathic pain is a prevalent and distressing problem faced by people with life-limiting illness that is often difficult to palliate. Gabapentin and pregabalin are widely prescribed as part of the routine approach to palliating neuropathic pain. Although they are often viewed as interchangeable agents, very little comparative data of their benefits and harms exists in clinical practice. Two previously reported pharmacovigilance studies that had used the same methodology for gabapentin and pregabalin were compared. These studies examined the benefits and harms of gabapentin and pregabalin after the medications had been routinely prescribed by clinicians working in a network of palliative care services using the same data collection tools with the same definitions and the same time points. Data were collected over 21 days from 282 patients prescribed either gabapentin or pregabalin for pain. Items included medication doses, pain scores, and adverse effects. In order to compare the medication responses, the final doses of pregabalin were converted to gabapentin does equivalents using previously published recommendations. The final pain scores were similar for both groups, and the reduction in pain were similar (OR = 11.2; 95 % CI 3.9, 32.7, p < 0.001). However, this was achieved at lower doses of gabapentin compared to pregabalin. Those receiving gabapentin were more likely to experience harms (OR = 3.5; 95 % CI 1.4, 9.1, p = 0.009) with the reported harms including somnolence, ataxia, nausea, tremor and nystagmus This hypothesis-generating work strongly supports the need for further trials to best delineate clinical differences in the GABA analogues.